An enantioselective synthesis of tarchonanthuslactone

Article abstract of DOI:10.1021/jo0163400

An enantioselective synthesis of tarchonanthuslactone has been achieved in eight steps from ethyl sorbate. The asymmetry of the route was introduced via a Sharpless asymmetric dihydroxylation allowing access to either enantiomer. The synthesis utilizes a palladium-catalyzed reduction and a diastereoselective base-catalyzed acetal formation as the key steps. The pyran ring of tarchonanthuslactone was established by a Still-olefination/lactonization sequence. DCC-mediated attachment of dihydrocaffeic acid completed the synthesis of tarchonanthuslactone in a 19% overall yield.

Full text of DOI:10.1021/jo0163400

2682
J . Org. Chem. 2002, 67, 2682-2685
Notes
An En a n tioselective Syn th esis of
Ta r ch on a n th u sla cton e
Sarah D. Garaas,† Thomas J . Hunter, and
George A. O’Doherty*
Department of Chemistry, University of Minnesota,
Minneapolis, Minnesota 55455
odoherty@chem.umn.edu
Received December 1, 2001
F igu r e 1.
Abstr a ct: An enantioselective synthesis of tarchonanthus-
lactone has been achieved in eight steps from ethyl sorbate.
The asymmetry of the route was introduced via a Sharpless
asymmetric dihydroxylation allowing access to either enan-
tiomer. The synthesis utilizes a palladium-catalyzed reduc-
tion and a diastereoselective base-catalyzed acetal formation
as the key steps. The pyran ring of tarchonanthuslactone
was established by a Still-olefination/lactonization sequence.
DCC-mediated attachment of dihydrocaffeic acid completed
the synthesis of tarchonanthuslactone in a 19% overall yield.
and Rychnovsky 13C NMR/acetonide analysis.7 Ulti-
mately, the structural studies for three of these struc-
tures (1-3) were confirmed by enantioselective total
synthesis.8
Tarchonanthuslactone (1) was isolated by Bohlmann
from Tarchonanthustrilobus compositae.9 Hsu et al. have
shown that tarchonanthuslactone lowers plasma glucose
in diabetic rats.10 Because of its interesting biological
activity, there have been several approaches to tarcho-
nanthuslactone (1).4b-f To date, all of these approaches
derive the asymmetry from the stoichiometric use of
either chiral auxiliaries or chiral reagents. For example,
Mori and co-workers synthesized 1 from a chiral dithiane
using a 16-step sequence.4a,b Solladie´ and co-workers
utilized a chiral sulfoxide to induce chirality during their
12-step synthesis of 1.4d More recently, Ramachandran
has used a reagent-controlled approach to 1 utilizing a
consecutive Ipc2Ballyl asymmetric allyl anion addition
to establish the relative stereochemistry of 1.4f All of the
above procedures for the synthesis of 1 involve the use
of stoichiometric reagents and/or substrates to control the
absolute asymmetry of tarchonanthuslactone.
We have been interested in the development of practi-
cal and concise enantioselective approaches to biologically
important substituted 1,3-polyol-5,6-dihydropyran-2-one-
containing natural products.3,11 These efforts have cul-
minated in an efficient route to cryptocarya diacetate (2)
from benzylidine-protected syn-3,5-dihydroxy carboxylic
ester 7 (Scheme 1).3,12 In our route to 2, asymmetry was
installed by the Sharpless asymmetric dihydroxylation
of the dienoate ethyl sorbate (8).13 As a model study for
the synthesis of the more complex even-numbered 1,3-
polyol/pyranone natural products (3 and 4), we decided
The 1,3-polyol/5,6-dihydro-2H-pyran-2-one motif is a
common structural unit found in several natural products
that possess a wide range of biological properties. These
biological activities include plant growth inhibition as
well as antifeedent, antifungal, antibacterial, and anti-
tumor properties.1,2 Due to the interest in their biological
activities, several synthetic approaches to these molecules
have been reported by us3 and others.4 The simplest
structure isolated with the syn-1,3-diol/5,6-dihydropyran-
2-one motif is the dihydrocaffeic ester, tarchonanthus-
lactone (1).4a,5 Some more complex examples of these
structures are cryptocarya diacetate (2), cryptocarya
triacetate (3), and passifloricin A (4) (Figure 1).6
The absolute and relative stereochemistries of tarcho-
nanthuslactone and the cryptocarya acetates have been
established by a combination of Mosher ester analysis
† University of Minnesota-NSF-REU Program Participant-2001.
(1) J odynis-Liebert, J .; Murias, M.; Bloszyk, E. Planta Med. 2000,
66, 199.
(2) Drewes, S. E.; Schlapelo, B. M.; Horn, M. M.; Scott-Shaw, R.;
Sandor, O. Phytochemistry 1995, 38, 1427.
(3) Hunter, T. J .; O’Doherty, G. A. Org. Lett. 2001, 3 (17), 2777.
(4) (a) Nakata, T.; Hata, N.; Iida, K.; Oishi, T. Tetrahedron Lett.
1987, 28, 5661. (b) Mori, Y.; Suzuki, M. J . Chem. Soc., Perkin Trans.
1 1990, 1809. (c) Mori, Y.; Kageyama, H.; Suzuki, M. Chem. Pharm.
Bull. 1990, 38, 2574. (d) Solladie´, G.; Gressot-Kempf Tetrahedron:
Asymmetry 1996, 7 (8), 2371. (e) J orgensen, K. B.; Suenaga, T.; Nakata,
T. Tetrahedron Lett. 1999, 40, 8855-8858. (f) Reddy, M. V. R.; Yucel,
A. J .; Ramachandran, P. V. J . Org. Chem. 2001, 66, 2512. (g) Gosh, A.
K.; Bilcer, G. Tetrahedron Lett. 2000, 41, 1003. (h) Boger, D. L.;
Ichikawa, D.; Zhong, W. J . Am. Chem. Soc. 2001, 123, 4161. (i) Reddy,
M. V. R.; Rearick, J . P.; Hoch, N.; Ramachandran, P. V. Org. Lett. 2001,
3, 19. (j) Smith, A. B.; Brandt, B. M. Org. Lett. 2001, 3, 1685.
(5) Echeverri, F.; Arango, V.; Quinones, W.; Torres, F.; Escobar, G.;
Rosero, Y.; Archbold, R. Phytochemistry 2001, 56, 881-885.
(6) (a) Andrianaivoravelona, J . O.; Sahpaz, S.; Terreaux, C.; Hostett-
mann, K.; Stoecki-Evans, H.; Rasolondramanitra, J . Phytochemistry
1999, 52, 265-269. (b) Echeverri, F.; Arango, V.; Quinones, W.; Torres,
F.; Escobar, G.; Rosero, Y.; Archbold, R. Phytochemistry 2001, 56, 881-
885.
(7) Collett, L. A.; Cavies-Coleman, M. T.; Rivett, D. E. A.; Drewes,
S. E.; Horn, M. M. Phytochemistry 1997, 44, 935-938.
(8) Cryptocarya acetates 1 and 2 were prepared by 16- and 24-step
routes, respectively, from the (S)-tert-butyl 3-hydroxybutyrate by
Nakata; see: ref 4e. Nakata has also prepared racemic tarchonan-
thuslactone and passifloricin A in 16 and 27 steps, respectively; see:
ref 4a. More recently, we have enantioselectively prepared 1 in 10 steps
and a 14% overall yield from ethylsorbate; see: ref 3.
(9) Bohlmann, F.; Suwita, A. Phytochemistry 1979, 18, 677.
(10) Hsu, F. L.; Chen, Y. C.; Cheng, J . T. Planta Med. 2000, 66,
228.
(11) (a) Harris, J . M.; O’Doherty, G. A. Tetrahedron 2001, 57, 5161-
5171. (b) Harris, J . M.; O’Doherty, G. A. Org. Lett. 2000, 2, 2983.
(12) Hunter, T. J .; O’Doherty, G. A. Org. Lett. 2001, 3 (7), 1049.
10.1021/jo0163400 CCC: $22.00 © 2002 American Chemical Society
Published on Web 03/23/2002

Notes
J . Org. Chem., Vol. 67, No. 8, 2002 2683
Sch em e 1
Sch em e 3
to apply this methodology toward an enantioselective
synthesis of tarchonanthuslactone (1).
hydroxyl groups were readily differentiated by taking
advantage of the fact that allylic carbonates are good
leaving groups for the formation of p-allyl palladium
complexes.18 Treatment of 12 with a catalytic amount of
palladium/triphenylphosphine (1.0% Pd2(dba)3‚CHCl3/
2.5% PPh3)19 and a mild hydride source (1:1, Et3N/
HCO2H) afforded an excellent yield (92%) of the desired
δ-hydroxy ester 13 with no loss of enantiomeric excess.
Exposing the δ-hydroxy enoate 13 to 3-4 equiv of
benzaldehyde and a catalytic amount of KOt-Bu (30-40
mol %) led to a 65% yield of the benzylidene-protected
3,5-dihydroxy carboxylic ester 7.20 Thus, the ester 7 was
conveniently prepared as a single diastereomer (>95%
de) in four steps and a 35% overall yield.
Specifically, we wanted to test the viability of con-
structing the pyranone ring in 6 from ester 7 by a three-
step sequence utilizing a Still cis-olefination14 and acid-
catalyzed lactonization. Critical for the successful imple-
mentation of this strategy was the discovery that acidic
conditions both deprotect the benzylidene acetal of 9 as
well as induce the resulting diol to selectively lactonize
to form pyranone 6 without catalyzing a subsequent 1,4-
addition to form bicyclic-lactone 10 (Scheme 2). Presum-
Sch em e 2
Having established a general procedure for the enan-
tioselective synthesis of either enantiomer of benzylidine
acetal 7, we turned our attention to the installation of
the pyranone functionality of tarchonanthuslactone. To
this end, we planned to convert ester 7 into the cis-enoate
9, which possesses all of the desired carbon atoms and
the correct double-bond stereochemistry of 1. The alde-
hyde 14 was easily prepared in a nearly quantitative
yield (>95%) by exposure of a THF solution of ester 7 to
1.1 equiv of DibalH at -78 °C (Scheme 4). Treatment of
ably, once a reliable procedure has been developed, it can
be applied toward the other even-numbered polyols such
as cryptocarya triacetate (3) and passifloricin A (4).
Herein, we describe our successful implementation of this
strategy toward the synthesis of the syn-1,3-diol-con-
taining tarchonanthuslactone (1). In addition, access to
the intermediate lactone 6 allows for access to the
enantiomer of the naturally occurring bicylic lactone 10
(Scheme 2).15
Sch em e 4
Following our previously reported protocol allowed
conversion of ethyl sorbate16 (8) into the protected diol 7
in four steps and a 35% overall yield (Scheme 3).12 The
sequence starts with a Sharpless dihydroxylation of ethyl
sorbate (8) yielding diol 11 in 85% yield. Either enanti-
omer of diol 11 can be obtained by Sharpless dihydroxy-
lation reactions with enantiomeric excesses on the order
of 80% from the (DHQ)2PHAL ligand system and >90%
from the (DHQD)2PHAL ligand.17
14 with the potassium salt of 15 afforded a 70% yield of
9 with a 9:1 double-bond cis/trans stereoselectivity.14
Having established the double-bond stereochemistry
and the C-5/C-7 stereocenters of tarchonanthuslactone
in 9, we looked to investigate the selective deprotection
The cyclic carbonate 12 was prepared by treating a
pyridine/CH2Cl2 solution of diol 11 with triphosgene,
providing 12 in a 95% yield. At this stage, the two
(13) For other approaches to syn-3,5-dihydroxy carboxylic esters,
see: (a) Miyazawa, M.; Matsuoka, E.; Sasaki, S.; Oonuma, S.;
Maruyam, K. Miyashita, M. Chem. Lett. 1998, 109. (b) Evans, D. A.;
Trotter, B. W.; Coleman, P. J .; Cote, B.; Dias, L. C.; Rajpakse, H. A.;
Tyler, A. N. Tetrahedron 1999, 55 (29), 8671-8726. (c) Solladie´, G.;
Wilb, N.; Bauder, C.; Bonini, C.; Viggiani, L.; Chiummiento, L. J . Org.
Chem. 1999, 64, 5447. (d) Sarraf, S. T.; Leighton, J . L. Org. Lett. 2000,
2, 3205-3208.
(14) Still, W. C.; Gennari, C. Tetrahedron Lett. 1983, 24, 4405.
(15) Takeda, Y.; Yoshihiro, O.; Toshiya, M.; Hirata, E.; Shinzato,
T.; Takishi, A.; Yu, Q.; Otsuka, H. Chem. Pharm. Bull. 2000, 48 (5)
752.
(17) All levels of enantioinduction were determined by HPLC
analysis (8% IPA/hexane, Chiralcel OD) and/or Mosher ester analysis.
(a) Sullivan, G. R.; Dale, J . A.; Mosher, H. S. J . Org. Chem. 1973, 38,
2143. (b) Yamaguchi, S.; Yasuhara, F.; Kabuto, K. T. Tetrahedron 1976,
32, 1363.
(18) (a) Tsuji, J .; Minami, I. Acc. Chem. Res. 1987, 20, 140. (b)
Hughes, G.; Lautens, M.; Wen, C. Org. Lett. 2000, 2, 107.
(19) This lower than normal (1.25:1 as opposed to 2:1) phosphine-
to-palladium ratio gave higher yields and faster reaction times.
(20) Evans, D. A. Gauchet-Prunet, J . A. J . Org. Chem. 1993, 58,
2446.
(16) The Aldrich Chemical Co. sells ethyl sorbate for $0.30/g.

2684 J . Org. Chem., Vol. 67, No. 8, 2002
Notes
Sch em e 5
of 6 with less than 5% of starting material 9 and/or
bicyclic lactone 10. At this stage, 6 was acylated first by
neutralization (solid NaHCO3) and solvent exchange
(CH2Cl2), followed by the addition of 1.1 equiv of DCC
and the carboxylic acid 17. This one-pot protocol for the
conversion of 9 to protected tarchonanthuslactone 18
provided an excellent yield (71%) of product with spectral
data identical to that of the material prepared by
Solladie´.4d
In conclusion, this highly enantio- and diastereocon-
trolled route illustrates the utility of our recently devel-
oped Os/Pd route to benzylidene-protected syn-1,3-diols.
The synthesis provides tarchonanthuslactone in eight
steps and 19% overall yield (82% average yield) and is
amenable to the preparation of either enantiomer by use
of asymmetric catalysis. Further studies on the use of
these chiral building blocks toward the synthesis of syn-
1,3-polyol-containing natural products such as 3 and 4
will be reported in due course.
and lactonization reaction sequence to convert enone 9
to pyranone 6 and not bicyclic lactone 10 (Schemes 2 and
5).21 In the course of our cryptocyara diacetate (2)
synthesis, we found that the benzylidene protecting group
could be easily removed by refluxing in 80% aqueous
acetic acid. These conditions were more troublesome
when applied to 9 in that refluxing enone 9 for 12 h in
80% aqueous acetic acid provided a nearly quantitative
yield of a 1:1 mixture of lactone 6 and bicyclic lactone
10.22 Reducing the reaction time along with careful
monitoring of the reaction mixture led to a more selective
conversion of 9 to diol 16.23 The penchant of diol 16 to
cyclization made it difficult to isolate in a pure form;
however, crude solutions of 16 were easy to prepare and
use. For instance, exposure of the crude diol 16 to cata-
lytic acid in THF at room temperature provided mixtures
of 6 and 10.24 Switching the reaction solvent from THF
to benzene proved to be a desirable solution. Hence,
treating the crude diol product 16 with catalytic amounts
of TsOH in benzene yielded lactone 6 (95%) with only
minor amounts of the undesired bicyclic lactone 10 (5%).
The hydroxylactone 6 that was prepared by this
sequence had spectral properties identical to that of the
material prepared by Solladie´.4d Following the Solladie´
procedure allowed acylation of pyranone 6 using 17 and
DCC to give 18, which was deprotected with TBAF to
give tarchonanthuslactone 1 (Scheme 6). While this
Exp er im en ta l Section 25
cis-E n oa t e (9). To a stirred solution of bis(2,2,2-trifluoro-
ethyl)methoxycarbonylmethylphosphonate (101 mg, 0.32 mmol)
and 18-crown-6 (212 mg, 0.8 mmol) in THF (1 mL) at -78 °C
was added KN(TMS)2 (0.48 mL of a 0.5 M solution in toluene).
The mixture was stirred for 1 h. The aldehyde 14, dissolved in
THF (1 mL), was added dropwise, and the resulting mixture was
stirred for 20 min. After this period, the reaction was quenched
with saturated sodium bicarbonate and warmed to room tem-
perature. The layers were separated, and the aqueous layer was
extracted with ether. The combined organic layers were washed
with brine and dried over anhydrous sodium sulfate. Removal
of the solvent and purification by silica gel chromatography
yielded 27 mg (72%) of a 9:1 mixture of the cis and trans esters:
Rf 0.61 (hexane/EtOAc, 4:1); [R]D -27.3 (c 0.80, CHCl3); IR (neat,
cm-1) 2973, 2855, 1723, 1648, 1439, 1405, 1379, 1339; 1H NMR
(CDCl3, 300 MHz) δ 7.53 (m, 2H), 7.37 (m, 3H), 6.49 (ddd, J )
11, 7.5, 7 Hz, 1H), 5.91 (ddd, J ) 11, 2, 2 Hz, 1H), 5.55 (s, 1H),
3.98 (m, 2H), 3.73 (s, 3H), 3.10 (dddd, J ) 16, 8, 4.5, 2 Hz, 1H),
2.91 (dddd, J ) 16, 7, 7, 2 Hz, 1H), 1.66 (ddd, J ) 13, 2.5, 2.5
Hz, 1H), 1.50 (ddd, J ) 13, 11, 11 Hz, 1H), 1.32 (d, J ) 6 Hz,
3H); 13C NMR (CDCl3, 75 MHz) δ 166.9, 146.1, 138.8, 128.8,
128.3, 126.3, 120.9, 100.9, 76.0, 73.1, 51.2, 38.3, 35.1, 21.7;
HRMS (CI) calcd for [C16H20O4 + H]+ 277.1440, found 277.1445.
Anal. Calcd for C16H20O4: C, 69.54; H, 7.30. Found: C, 69.15;
H, 7.51.
Sch em e 6
TBS-P r otected Ta r ch on a n th u sla cton e (18).26 A solution
of cis-enoate 9 (12 mg, 0.043 mmol, 1.9 mL 80% AcOH) was
heated to 60 °C and stirred for 4 h. The solvent was then
removed under reduced pressure, and 1 mL of benzene along
with 1 mg of p-toluenesulfonic acid was added to the flask. The
reaction mixture was stirred for 2 h when solid sodium bicarbon-
ate was added to the reaction. The solution was filtered through
a plug of glass wool, and the solvent was removed under reduced
pressure and replaced with methylene chloride (1 mL). To this
solution were added 27.5 mg (0.067 mmol) of TBS-protected
dihydrocaffeic acid,13 13 mg (0.067 mmol) of DCC, and catalytic
DMAP (<1 mg). This reaction was stirred for 3 h. Ether was
added to the solution, and the mixture was filtered through a
pad of Celite. Removal of the solvent under reduced pressure
provided crude 18. Purification of the crude material with silica
gel chromatography yielded TBS-protected tarchonanthuslactone
18 (17 mg, 71% yield for the three steps): Rf 0.42 (hexane/EtOAc,
4:1).
three-step procedure provided adequate yields of 18 from
9, a simpler and higher-yielding procedure for the conver-
sion of 9 to 18 was accomplished with a one-pot proce-
dure. Thus, after the deprotection of 9 to produce diol
16, the solvent (AcOH) was switched to benzene and a
catalytic amount of TsOH was added producing a solution
(23) At this stage of the reaction, there can be a small amount of
compound 6 detected.
(24) These procedures provide a ca. 50% yield of 10; however, no
efforts were made to optimize this procedure for the production of 10.
(25) For full experimental details for all compounds shown and
general experimental details, see Supporting Information.
(26) These data match spectral data for the compounds reported in
ref 4d.
(21) Others have had success at removing an acetonide protecting
group to provide 16; see: ref 4d.
(22) Hayakawa, H.; Miyashita, M. Tetrahedron Lett. 2000, 41, 707.

Notes
NMR Da ta for Agylcon (6):26 1H NMR (CDCl3, 200 MHz) δ
J . Org. Chem., Vol. 67, No. 8, 2002 2685
Ta r ch on a n th u sla cton e (1).26 Benzoic acid (5 mg, 0.044
mmol) was added to a solution of protected tarchonanthuslactone
(8 mg, 0.015 mmol) and THF (1 mL). A 1.0 M solution of TBAF
in THF (30 µL) was added to the solution. The mixture was
stirred at room temperature for 2 h. The solvent was evaporated
and extracted with ethyl acetate (3 × 5 mL). Evaporation of the
solvent and purification by silica gel chromatography yielded
tarchonanthuslactone (4 mg, 85% yield): Rf 0.3 (ether), 1H NMR
(CDCl3, 300 MHz) δ 6.85 (ddd, J ) 10, 6, 3 Hz, 1H), 6.77 (d, J
) 8 Hz, 1H), 6.75 (d, J ) 3 Hz, 1H), 6.62 (dd, J ) 8, 2.5 Hz, 1H),
6.02 (ddd, J ) 10, 3, 1 Hz, 1H), 5.07 (ddq, J ) 10, 6, 4 Hz, 1H),
4.17 (dddd, J ) 11.5, 6.5, 6, 4.5 Hz, 1H), 2.86 (t, J ) 7 Hz, 2H),
2.63 (t, J ) 7 Hz, 2H), 2.36 (dddd, J ) 18, 4, 4, 1 Hz, 1H), 2.24
(dddd, J ) 18, 11.5, 3, 3 Hz, 1H), 2.08 (ddd, J ) 14.5, 8.5, 6 Hz,
1H), 1.77 (ddd, J ) 14.5, 7, 4 Hz, 1H), 1.27 (d, J ) 6 Hz, 3H).
6.89 (ddd, J ) 10, 4.4, 3.8 Hz, 1H), 6.02 (ddd, J ) 10, 2, 2 Hz,
1H), 4.64 (dddd, J ) 8, 8, 8, 5 Hz, 1H), 4.10 (ddq, J ) 8.4, 6.4,
4.2 Hz, 1H), 2.37-2.44 (m, 2H), 2.01 (ddd, J ) 14, 8, 8 Hz, 1H),
1.76 (ddd, J ) 14.4, 5.2, 4.2 Hz, 1H), 1.26 (d, J ) 6 Hz, 3H); 13
C
NMR (CDCl3, 75 MHz) δ 164.1, 145.4, 121.3, 76.7, 65.4, 43.6,
29.6, 23.8.
NMR Da ta for Bicyclic Com p ou n d 10:27 1H NMR (1:1
CDCl3-C6D6, 300 MHz) δ 4.39 (dddd, J ) 4, 4, 4, 2 Hz, 1H),
3.88 (m, 1H), 3.67 (ddq, J ) 12, 6, 3 Hz, 1H), 2.59 (br d, J ) 19
Hz, 1H), 2.30 (dd, J ) 19, 5.4 Hz, 1H), 1.67 (br d, J ) 13.8 Hz,
1H), 1.47 (dddd, J ) 14, 4, 2, 2 Hz, 1H), 1.32 (dddd, J ) 14, 4,
2, 2 Hz, 1H), 1.10 (m, 1H), 0.98 (d, J ) 6 Hz, 3H); 13C NMR
(CDCl3, 125 MHz) δ 169.9, 73.2, 65.9, 62.0, 38.6, 36.5, 29.6, 21.4.
NMR Da t a for TBS-P r ot ect ed Ta r ch on a n t h u sla ct on e
(18):26 1H NMR (CDCl3, 500 MHz) δ 6.85 (ddd, J ) 10, 5.5, 2.5
Hz, 1H), 6.72 (d, J ) 8 Hz, 1H), 6.64 (m, 2H), 6.01 (ddd, J ) 9.5,
2, 1 Hz, 1H), 5.10 (ddq, J ) 8, 6, 4.5 Hz, 1H), 4.42 (dddd, J )
13, 6.5, 6.5, 4 Hz, 1H), 2.81 (t, J ) 8 Hz, 2H), 2.55 (t, J ) 8 Hz,
2H), 2.35 (dddd, J ) 18.5, 4.5, 4.5, 1 Hz, 1H), 2.26 (dddd, J )
18, 11.5, 3, 3 Hz, 1H), 2.16 (ddd, J ) 14, 8.5, 6 Hz, 1H), 1.81
(ddd, J ) 14.5, 6.5, 4 Hz, 1H), 1.26 (d, J ) 6.5 Hz, 3H), 0.98 (s,
9H), 0.97 (s, 9H), 0.19 (s, 6H), 0.18 (s, 6H); 13C NMR (CDCl3,
125 MHz) δ 172.5, 163.9, 146.6, 145.2, 144.8, 133.4, 121.4, 121.2,
121.1, 120.9, 74.9, 67.1, 40.8, 36.2, 30.2, 29.1, 25.9, 20.3, 18.4,
-4.1.
Ack n ow led gm en t. We thank the Arnold and Mabel
Beckman Foundation for their generous support of our
program.
Su p p or tin g In for m a tion Ava ila ble: Complete experi-
mental procedures and spectral data for the known compounds
prepared by this route. This material is available free of charge
via the Internet at http://pubs.acs.org.
(27) These data match spectral data for the enatiomer of compound
10 as reported in ref 15.
J O0163400